P2X7R is an ATP-gated ion channel belonging to the P2X ionotropic channel family. The gene was first isolated from rat brain (Surprenant et al. (1996) 272:735-738) and subsequently from a human monocyte library (Rassendren et al. (1997) J. Biol. Chem. 272:5482-5486; Genbank accession numbers NM—002562, Y09561) by virtue of its sequence homology with the other members of the P2X family. It was later found that P2X7R corresponded to the unidentified P2Z receptor which mediates the permeabilising action of ATP on mast cells and macrophages (Dahlqvist and Diamant (1974) Acta Physiol. Scand. 34:368-384; Steinberg and Silverstein (1987) J. Biol. Chem. 262:3118-3122; Gordon (1986) Biochem. J. 233:309-319). The P2X7R has two hydrophobic membrane-spanning domains, an extracellular loop, and forms transmembrane ion channels. P2X7R bears a pharmacological profile markedly different from other P2X homo- or heteromers (North and Surprenant (2000) Annual Rev. Pharmacology Toxicology 40:563-580). P2X7R requires levels of ATP in excess of 1 mM to achieve activation, whereas other P2X receptors activate at ATP concentrations of ≦100 μM (Steinberg et al. (1987) J. Biol. Chem. 262:8884-8888; Greenberg et al. (1988) J. Biol. Chem. 263:10337-10343). While all P2X receptors demonstrate non-selective channel-like properties following ligation, the channels formed by the P2X7R can rapidly transform into pores that can allow the passage of molecules of up to 900 Dalton (Virginio et al. (1999) J. Physiol. 519:335-346).
P2X7R is expressed in haematopoietic cells, mast cells, lymphocytes, erythrocytes, fibroblast, Langerhans cells, and macrophages (Surprenant et al., 1996, Science 272:3118-3122). In the central nervous system, P2X7R expression has been reported in glial cells, Schwann cells, astrocytes, as well as in neurons (Ferrari et al. (1996) J. Immunol 156:1531-1539; Collo et al. (1997) Neuropharmacology 36: 1277-1283; Anderson and Nedergaard (2006) Trends Neuroscien 29: 257-262).
P2X7R is involved in the regulation of the immune function and inflammatory response. Activation of P2X7R by ATP in macrophages is associated with mitogenic stimulation of T cells (Baricordi et al. (1996) Blood 87:682-690), the release of cytokines (Griffiths et al. (1995) J. Immol. 154:2821-2828), and formation of macrophage polykarions (Falzoni et al. (1995) J. Clin. Invest. 95:1207-1216). P2X7R is involved in the processing and release of active interleukin-1beta (IL-1β) from proinflammatory cells (Perregaux and Gabel (1998) J Biol Chem 269:15195-15203; Ferrari et al., (2006) J Immunol 176: 3877-3883). Stimulation of the P2X7R by ATP can also result in apoptosis and cell death by triggering the formation of non-selective plasma membrane pores (Di Virgilio et al. (1998) Cell Death Differ. 5:191-199).
Upregulation of P2X7R has been observed during ischemic damage and necrosis induced by occlusion of middle cerebral artery in rat brain (Collo et al. (1997) Neuropharmacol 36:1277-1283). Recent studies indicate a role of P2X7R in the generation of superoxide in microglia, and upregulation of P2X7R has been detected around amyloid plaques in a transgenic mouse models for Alzheimer's disease (Parvathenani et al. (2003) J Biol Chem 278:13300-13317) and in multiple sclerosis lesions from autopsy brain sections (Narcisse et al. (2005) Glia, 49:245-258).
Studies from mice lacking P2X7R resulted in absence of inflammatory and neuropathic hypersensitivity to mechanical and thermal stimuli, indicating a link between P2X7R and inflammatory and neuropathic pain (Chessell et al. (2005) Pain 114:386-396). Antagonists of P2X7R significantly improved functional recovery and decreased cell death in spinal cord injury in animal models (Wang et al. (2004) Nature Med 10:B21-B27).
Compounds which modulate P2X7R have been reported. For example, Brilliant Blue (Jiang et al., Mol. Phamacol. 58 (2000), 82-88), the isoquinolines 1-[N,O-Bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine and N-[1-[N-methyl-p-(5 isoquinolinesulfonyl)benzyl]-2-(4 phenylpiperazine)ethyl]-5-isoquinolinesulfonamide (Humphreys et al., Mol. Pharmacol., 54 (1998), 22-32), adamantane derivatives (WO 99/29660, WO 99/29661, WO 00/61569, WO 01/42194, WO 01/44170, WO 01/44213, WO 01/94338, WO 03/041707, WO 03/042190, WO 03/080579, WO 04/074224, WO 05/014529, WO 06/025783, WO 06/059945), piperidine and piperazine compounds (WO 01/44213, WO 01/46200, WO 08/005,368), benzamide and heteroarylamide compounds (WO 03/042191, WO 04/058731, WO 04/058270, WO 04/099146, WO 05/019182, WO 06/003500, WO 06/003513, WO 06/067444), substituted tyrosine derivatives (WO 00/71529, WO 03/047515, WO 03/059353), imidazole compounds (WO 05/014555), amino-tetrazoles compounds (WO 05/111003), cyanoamidine (WO 06/017406), bicycloheteroaryl derivatives (WO 05/009968, WO 06/102588, WO 06/102610, WO 07/028.022, WO 07/109,154, WO 07/109,160, WO 07/109,172, WO 07/109,182, WO 07/109,192, WO 07/109,201), acylhydrazide (WO 06/110516), and other examples (WO 99/29686, WO 04/106305, WO 05/039590, WO 06/080884, WO 06/086229, WO 06/136004, WO 07/025,366, WO 07/056.046, WO 07/056.091, WO 07/141,267, WO 07/141,269, WO 08/003,697) are antagonists of P2X7R while Oxidized ATP (oATP) acts as an irreversible inhibitor of the receptor (Chen et al., J. Biol. Chem., 268 (1993), 8199-8203).
Consequently, there is strong evidence that compounds acting on P2X7R can be used in the treatment of pain, inflammatory processes, and degenerative conditions associated with disease states such as rheumatoid arthritis, osteoarthritis, psoriasis, allergic dermatitis, asthma, chronic obstructive pulmonary disease, airways hyper-responsiveness, septic shock, glomerulonephritis, irritable bowel disease, inflammatory bowel disease, Crohn's disease, ulcerative colitis, atherosclerosis, growth and metastases of malignant cells, myoblastic leukaemia, diabetes, Alzheimer's disease, Parkinson's disease, multiple sclerosis, glaucoma, depression, bipolar affective disorders, anxiety, meningitis, traumatic brain injury, acute spinal cord injury, neuropathic pain, osteoporosis, burn injury, ischemic heart disease, myocardial infarction, stroke, and varicose veins.
Thus, the object on the present invention is to provide a novel series of compound which can inhibit P2X7R activity and can be used in the treatment of the above mentioned diseases.